Potentiometric DNA sensing platform using redox-active DNA probe pair for sandwich-type dual hybridization at indicator electrode surface

• A potentiometric DNA sensor enables real time hybridization analysis is described.
• Redox-active DNA conjugates having either ferrocene or ferroin were synthesized.
• Dual-hybridization of target by the redox-active DNA pair produced emf responses.
• As the model target, detection of one of the human oncogenes, K-ras was demonstrated.
• Kinetic analysis of the emf response determined the hybridization rate constant.

A potentiometric sensing platform that enables real-time DNA hybridization detection is described. A model target DNA, t37s: 5′-AAA AAA AAA AAA-(TC)2-Ts5-(TC)2-GGA GCT GGT GGC-3′, which consist of a dodecamer polydeoxyadenylic acid and the human K-ras oncogene, and a five-successive deoxythymidine phosphorothioate (Ts) was designed. With the gold–phosphorothioate binding, the DNA could bind the complementarily sequences to concentrate them at the gold electrode surfaces. Accordingly, a dodecamer polydeoxythymidylic acid having ferroin-moiety (T12FeP) and a ferrocene-modified complementary of K-ras (KrasFc) were synthesized. Electrochemical quartz-crystal-microbalance (QCM) using Au-sputtered quartz chips that served as the indicator electrode collected the electrode responses. When the electrode surface was treated with the T12FeP–hybridized t37s, which were subsequently oxidized to the corresponding Fe(III) form, the emf developed in a buffer solution responded to KrasFc; with the electrode-attached t37s the redox-active DNAs could group into a pair to establish specific redox-titration equilibrium. A QCM confirmed the on-electrode titrimetry feasible by determining the initial concentration and the amount of hybridization along with the emf measurements. Although the present method is necessary for two-kinds of redox conjugation of the target DNA, it should be important as a novel framework of electrochemical gene sensing. Preliminary examples of real-time measurement were also demonstrated with the results of kinetics analysis data.